Automotive crash protection systems are well-known in the automotive industry. Crash protection systems generally fall into one of two categories; namely, active and passive restraints. Passive restraints include systems such as air bags where the deployment of the crash protection mechanism is initiated by the system. Active restraints, for instance manual type seat belts, are not deployed on initiative of the crash protection system, but are engaged by the operator. Both passive and active restraint systems are optimized to protect a range of adult occupant sizes. To service the need of protecting children in the event of a crash, child seats were developed to be used in conjunction with seat belt systems to properly restrain children. One of the most important parameters in installing child seats is the tension on the seat belt used to fasten the child restraint in the vehicle. However, the general public does not have a convenient means to determine if proper seat belt tension is provided upon installation of a child seat.
Typically, a seat belt system is provided for restraining a child seat having an automatic locking retractor (ALR) function. This mode causes the retractor to act as a one-way clutch, allowing the belt to be retracted but not extended from the retractor. Proper belt tension is achieved by feeding the webbing into the retractor, thus compressing the seat cushion until the proper tension level is achieved.
National statistics show that over 80% of the child seat installations made today are made incorrectly. It is estimated that over one third of incorrectly installed child seats are the result of improper seat belt tension. Seat belts in automobiles are designed to restrain the passenger within the vehicle. Sufficient belt tension is required to ensure that the child seat does not move, rock, or rotate out of the preferred installation position, and to ensure that the child seat operates properly in a dynamic crash event. Currently, child seat installations are judged acceptable based on a feeling, not a measurement. The general public is faced with the problem of not objectively knowing when adequate belt tension has been applied. Ideally, a system for measuring seat belt tension would be useable for existing vehicles without requiring that it be especially adapted for a specific vehicle design.